Integrated optical devices for directly processing optical signals have become of greater importance as optical fiber communications increasingly replace metallic cable and microwave transmission links. Integrated optical devices can advantageously be implemented as silica optical circuits having compact dimensions at relatively low cost. Silica optical circuits employ integrated waveguide structures formed on silicon substrates.
In some applications, optical gratings are formed in the silicon substrate or chip for input-output of the photonic signal. Typically, the optical grating is formed as a grating coupler on a major surface of the silicon substrate and connects via optical circuits to an integrated optical device, for example, an optical multiplexer or demultiplexer as a passive device or optical amplifier as an active device.
During manufacture, the integrated optical devices are typically tested as a device under test (DUT) using a test probe device to determine whether the DUT is acceptable or should be rejected. Passive devices typically have been measured by cascading a large number of DUTs so that the power loss of the cascaded DUTs is large enough compared to any loss at the grating couplers resulting from misalignment of the test probe device onto the grating couplers. This has been found expensive and cumbersome since many DUTs are typically cascaded.